1. Field of the Invention
The present invention relates to a photosensitive compound, a photosensitive composition containing the photosensitive compound dissolved in a solvent, a method for resist pattern formation by use of the photosensitive composition, and a process for producing a device by the method for the resist pattern formation.
2. Description of the Related Art
In recent years, for fine working in semiconductor and other electronic device industries, higher density and higher integration in the devices are required. In the semiconductor device production process, photolithography is an important technique in fine pattern formation.
The photolithography employs essentially a technique for stable fine working to a precision of 100 nm or finer. Therefore, the resist used in the photolithography should enable formation of a pattern to a precision of 100 nm or finer.
Diazonaphthoguinone-novolak type resists are widely used. These resists utilize a dissolution inhibition effect of the diazonaphthoquinone compound on a phenol resin (U.S. Pat. No. 4,859,563).
A diazonaphthoquinone-novolak type resist constituted of a low-molecular phenol resin cannot be affected by the dissolution inhibition effect of the naphthoquinone compound, resulting in a low development contrast between exposed regions and unexposed regions.
Lately, chemically amplified resists are used as a high-resolution resist rather than the diazonaphthoquinone-novolak type resist. In the chemically amplified resist, an acid (H+) is generated by irradiation with an active ray, and the generated acid catalyzes the deprotection reaction of an alkali-solubilizing group protected by an acid-decomposable protecting group to make the resist soluble in alkali (Journal of Photopolymer Science and Technology 17, 435, (2004)).
In formation of a resist pattern of a chemically amplified resist, the resist is heat-treated prior to the development in order to accelerate the deprotection reaction catalyzed by the acid generated in the exposed region.
In this heat treatment, the acid is allowed to diffuse to a distance of about 10 nm by the heat (“Proc. SPIE”, 6154, 710, 2006). This diffusion of the acid causes fine roughness at the edge portions of the pattern, namely line edge roughness (LER), to lower the resolution.
The LER depends also on the molecular weight of the base compound. The base compound herein denotes a compound having an alkali-solubilizing group or a protected alkali-solubilizing group in the resist composition.
Since the base compound dissolves, molecule by molecule, into the developing solution, a larger molecular weight of the base compound causes larger LER.
A base compound of a lower molecular weight has a lower glass transition temperature and a lower melting point. When the chemically amplified resist is heated before the development treatment at a temperature higher than its glass transition temperature, the formed acid diffuses to a longer distance to lower the resolution.
Therefore, the base compound of the chemically amplified resist should have a glass transition temperature higher than the deprotection reaction temperature under acid catalysis. This requirement limits the design of the chemically amplified resist for a lower LER (line edge roughness) by use of a lower molecular-weight resist.
The inventors of the present invention found that, in a pattern formation by near-field light exposure, when a chemically amplified resist diluted with an organic solvent is applied in a thickness of 10 nm, the LER of the resulting resist pattern is larger undesirably.
J. Org. Chem. 2003, 68, 9100 (2003) discloses a caged compound having a latent physiological activity formed by nitrobenzyl-etherifying the phenolic hydroxyl group of capsaicin. This compound is not intended for use as a pattern-forming material.
J. Appl. Polym. Sci., 33, 1763 (1987) discloses a photosensitive polyimide resist having a nitrobenzyl group. This resist can be made alkali-soluble by light irradiation to eliminate the nitrobenzyl from the polyimide. The polymer of this resist is solubilized by elimination of the nitrobenzyl to form a carboxylic acid group (COOH). However, this resist gives resolution of as low as a micrometer order owing to swelling of the resist polymer caused by the reaction of the carboxylic acid with the alkali developing solution.